1. Field of the Invention
The present invention relates to disk drives and more particularly to a technique for improving utilization of partially defective data tracks in a disk drive.
2. Description of the Prior Art
In order to remain competitive, disk drive manufacturers must continually provide increased data storage capacity while rigidly controlling disk drive manufacturing cost. One key to increased storage capacity is increased track density, often expressed as tracks per inch or TPI. Market demand for increased storage capacity has pushed disk drive designers to increase the TPI of disk drives. The increased TPI has resulted in tighter track tolerances. During initial configuration of a disk drive by the manufacturer, a track that is not completely within tolerance is skipped and eventually replaced by a spare track set aside for such purpose. Setting aside a sufficient number of spare tracks to insure that the disk drive yields a desired capacity tends to conflict with the demand for increased storage capacity.
Accordingly, there exists a need for a technique that enables a disk drive to minimize the need for setting aside and using spare tracks for replacing tracks that are not completely within tolerances, without unnecessarily increasing the disk drive""s manufacturing cost. The present invention satisfies this need.
The present invention may be embodied in a method and a disk drive for improving data storage capacity of concentric data tracks on a rotating disk of the disk drive. Each data track includes a plurality of embedded servo wedges separating a plurality of data wedges. In the method, a servo-fault position threshold is established for aborting a write operation if a transducer head position error from a circular track centerline exceeds the servo-fault position threshold. Servo wedges having defects are tagged, and during a track following operation, the servo-fault position threshold is ignored at a tagged servo wedge thereby preventing the tagged servo wedge from aborting a write operation. The write operation is prevented for a predetermined number of servo wedges immediately following the tagged servo wedge by skipping data wedges between the tagged servo wedge and a last servo wedge of the predetermined number of servo wedges. Data is then written to a data wedge immediately following the last servo wedge.
In a more detailed feature of the invention, the method may include storing location information for the tagged servo wedges in read/writeable non-volatile semiconductor memory or in reserved data wedges on the disk. The stored location information for the tagged servo wedges may be transferred to dynamic random access memory for the track following operation. The predetermined number of servo wedges may be between about 7 and 10 for a track having more than about 70 embedded servo wedges. A servo wedge may be tagged if the servo wedge has a position from a respective circular track centerline that is greater than the servo-fault threshold or if it includes an embedded data error. Data segments may be located in the data wedges independently of locations of the servo wedges.